Investigation of the effect of plant density on growth indices of different cultivars of rapeseed (Brassica napus L.) in Mazandaran climatic conditions

One of the strategies to increase the yield per unit area is to use suitable cultivars that are compatible with the climatic conditions of each region at the appropriate planting density, so that there is minimal competition between plants. Determining the appropriate crop density for rapeseed cultivars is very important and plays a decisive role in achieving the desired yield. Planting the crop for each plant and cultivar should be done in a density where the plant is well emerge, establish and in each stage of growth, has enough space to maximize the use of environmental factors and not face unfavorable conditions as much as possible.

This factorial experiment was conducted in a randomized complete block design in research farm of Gharakhil Agricultural Research Center, Ghaemshahr in 2017-2018. Treatments included: densities of 42, 66, 88, 114 and 133 plants m-2 and four rapeseed cultivars including: Hyola 401, Agamax, Hyola 4815 and Trapper which were performed in three replications. The evaluated traits included growth indices such as total dry matter content, leaf area index, crop growth rate, relative growth rate and net photosynthesis rate as well as yield.

The results showed that the interaction effect of cultivar and plant density was significantly different only for total dry matter and leaf area index. Maximum amount of total dry matter (910 g m-2) and leaf area index (3.53) was observed in Hayola 401 cultivar and density of 88 plants m-2 and minimum amount of total dry matter (393 g m-2) and leaf area index (2.26) was observed in Trapper cultivar at a density of 42 plants m-2. According to the results, the only simple effect of density was significant on crop growth rate, relative growth rate and net photosynthesis rate, according to which the highest crop growth rate with an average of 11.36 g m-2 d-1 was related to the density of 88 plants m-2 and the lowest one was obtained with an average of 5.91 g m-2 d-1 from a density of 42 plants m-2. Also, the maximum relative growth rate and net photosynthesis rate with an average of 0.0580 g g-1 d-1 and 3.49 g m-2 were obtained at a density of 88 plants m-2, respectively, and their minimum ones with an average of 0.0530 g g-1 d-1 and 2.99 g m-2 was seen from the density of 42 plants m-2. The highest grain yield with an average of 7031.8 kg ha-1 was related to Hayola 401 cultivar in a density of 88 plants m-2.

With increasing density of 42 plants m-2, dry matter production and leaf area increased; when the highest amount of dry matter and leaf area index in cultivar Hayola 401 in density of 88 plants m-2 had the best results and the highest rate of crop growth rate, relative growth rate and net photosynthesis rate were obtained at density of 88 plants m-2. Therefore, in low densities, due to the lack of complete canopy closure and low surface for radiation absorbance (leaves), dry matter production had decreased, while with increasing density more than 88 plants.m-2 due to increase intra specific competition, dry matter production and leaf area index decreased. Therefore, according to the results, planting cultivars Hayola 401 at a density of 88 plants m-2 is recommended to achieve high yields in the climate of Mazandaran.